It has long been recognized that electrical current will induce a magnetic field, and that a moving magnetic field can induce current, or changes in the magnitude of a pre-existing current. One conventional application of this phenomenon is the transducer for converting between current and vibration. More particularly, a transducer for converting between vibration and current can: (1) convert linear mechanical vibration (e.g., acoustic vibration) into a pattern of variations in electrical current; and/or (2) convert variations in a current into vibration. One type of transducer is an accelerometer, which uses the acceleration characteristics of mechanical vibrations in its transduction between vibration and electrical signal.
Generally speaking, the most common geometry for this kind of transducer is a current carrier suspended in proximity to a magnet so that the current carrier and magnet can vibrate relative to each other in a linear direction. If external vibration induces the magnet and the current carrier to move relative to each other, then a current will be induced in the current carrier. If current is supplied to the current carrier from a current source, then the supplied, nominal current is subject to change in magnitude and/or direction by the vibration of the magnetic field. If relative linear vibration of the current carrier and magnet can be induced by external vibrations having a frequency in the acoustic range, then the transducer can be used as a microphone. In a microphone, the current changes in the current carrier may be recorded onto a recording medium or transduced back into acoustic vibrations. Using the current patterns generated by a microphone transducer, sound can be recorded or transmitted across long distances.
Moving to current-to-vibration transduction, an external current source may supply a variable amount of current (e.g., an alternating current) to the current carrier. This will induce the current carrier and the magnet to vibrate relative to each other in a linear direction. If the induced vibration is in the acoustic range, then sound will be produced by the transduction of the current.
Probably the most popular geometry for these transducers is the use of a coil shaped current carrier wrapped around a permanent magnet, with either the coil or the magnet being fixed to some type of housing (e.g., microphone housing, speaker housing). The unfixed component (referred to as the moving component) is partially constrained so that it is free to vibrate in the direction along the central axis of the coil. The moving component or components (depending upon whether both the coil and magnet move) are generally attached to the transducer housing by some type of elastic member that acts as a spring. Also, a diaphragm may be fixed to the moving component to either: (1) better pick up external vibrations from the surroundings (in a microphone); or (2) better transmit induced vibration to the surroundings (in a speaker).
One application for these types of transducers is a geophone for measuring seismic vibrations in the surface of a planet. Another conventional application of the above-discussed type of transducer is the use of the transducer in a guitar. In a guitar, taut strings are vibrated to induce acoustic vibrations in the guitar body and the air surrounding the guitar. A transducer is fixed to some part of the guitar. The vibrations of the guitar induce relative vibration between a coil and a permanent magnet in the transducer. This induced relative vibration causes current patterns in the coil. The current in the coil is usually amplified and sent to a speaker to produce louder and better-directed sound corresponding to the vibration of the guitar.
Examples of transducers for converting between linear vibration and current are shown in the following U.S. patent numbers: (1) U.S. Pat. No. 3,725,561 (“Paul”); (2) U.S. Pat. No. 4,010,334 (“Demeter”); (3) U.S. Pat. No. 4,504,932 (“Sundt”); (4) U.S. Pat. No. 4,237,347 (“Burundukov et al.”); (5) U.S. Pat. No. 5,276,276 (“Gunn”); (6) U.S. Pat. No. 5,461,193 (“Schertler”); and (7) U.S. Pat. No. 5,641,932 (“Lace”). These patents are herein incorporated by reference. These examples provide some idea of the wide variety of structural details that transducers for converting between current and sound may exhibit.
To the extent that specific publications are discussed above, these discussions should not be taken as an admission that the discussed publications (e.g., patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time and/or sufficiently enabling so as to amount to prior art for patent law purposes.